Bilateral device, system and method for monitoring vital signs

ABSTRACT

The invention features a monitoring device that measures a patient&#39;s vital signs (e.g. blood pressure). The device features a first sensor configured to attach to a first portion of the patient&#39;s body that includes: i) a first electrode configured to generate a first electrical signal from the first portion of the patient&#39;s body; ii) a first light-emitting component; and iii) a first photodetector configured to receive radiation from the first portion of the patient&#39;s body after the radiation is emitted by the first light-emitting component and in response generate a first optical waveform. The device also features a second sensor that includes essentially the same components. An amplifier system, in electrical contact with the first and second electrodes, receives first and second electrical signals from the two sensors to generate an electrical waveform. A processor, in electrical contact with the amplifier system, receives the electrical waveform, the first optical waveform, and the second optical waveform. The processor runs computer code that processes the input waveforms with an algorithm to determine at least one of the patient&#39;s vital signs.

CROSS REFERENCES TO RELATED APPLICATION

This Application is a Continuation of U.S. Ser. No. 11/420,281, filedMay 25, 2006.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and system for measuring vitalsigns, and particularly blood pressure, from a patient.

2. Description of the Related Art

Pulse oximeters are medical devices featuring an optical module,typically worn on a patient's finger or ear lobe, and a processingmodule that analyzes data generated by the optical module. The opticalmodule typically includes first and second light sources (e.g.,light-emitting diodes, or LEDs) that transmit optical radiation at,respectively, red (λ˜600-700 nm) and infrared (λ˜800-1200 nm)wavelengths. The optical module also features a photodetector thatdetects transmitted radiation that passes through an underlying arterywithin, e.g., the patient's finger or earlobe. Typically the red andinfrared LEDs sequentially emit radiation that is partially absorbed byblood flowing in the artery. The photodetector is synchronized with theLEDs to detect the transmitted radiation. In response, the photodetectorgenerates a separate radiation-induced signal corresponding to eachwavelength. The signal, called a plethysmograph, varies in atime-dependent manner as each heartbeat varies the volume of arterialblood and hence the amount of radiation absorbed along the path of lightbetween the LEDs and the photodetector. A microprocessor in the pulseoximeter digitizes and processes plethysmographs generated by the redand infrared radiation to determine the degree of oxygen saturation inthe patient's blood using algorithms known in the art. A number between94%-100% is considered normal, while a number below 85% typicallyindicates the patient requires hospitalization. In addition, themicroprocessor analyzes time-dependent features in the plethysmograph todetermine the patient's heart rate.

Another medical device called an electrocardiograph features conductiveelectrodes, placed at various locations on a patient's body, thatmeasure electrical signals which pass into an amplification circuit. Thecircuit generates a waveform called an electrocardiogram, or ECG, thatdescribes a time-dependent response of the patient's cardiovascularsystem.

Various methods have been disclosed for using both plethysmographs andECGs, taken alone or in combination, to measure arterial blood pressure.One such method is disclosed in U.S. Pat. No. 5,140,990 to Jones et al.The '990 Patent discloses using a pulse oximeter with a calibratedauxiliary blood pressure measurement to generate a constant that isspecific to a patient's blood pressure.

Another method for using a pulse oximeter to measure blood pressure isdisclosed in U.S. Pat. No. 6,616,613 to Goodman. The '613 Patentdiscloses processing a pulse oximetry signal in combination withinformation from a calibrating device to determine a patient's bloodpressure.

U.S. Pat. Nos. 5,857,795 and 5,865,755 to Golub each discloses a methodand device for measuring blood pressure that processes a time differencebetween points on an optical plethysmograph and an ECG along with acalibration signal.

U.S. Pat. No. 6,511,436 to Asmar discloses a device for evaluatingarterial wall stiffness by using pulse wave velocity measurements. Thedevice estimates blood pressure using pulse wave velocity and apatient's biometric parameters.

Chen et al, U.S. Pat. No. 6,599,251, discloses a system and method formonitoring blood pressure by detecting plethysmographs at two differentlocations on a subject's body, preferably on the subject's finger andearlobe. The plethysmographs are detected using conventional pulseoximetry devices and then processed to determine blood pressure.

Inukai et al., U.S. Pat. No. 5,921,936, discloses a system that uses anelectrocardiogram to detect the start of a heart beat and uses a cuffequipped with a pressure sensor to detect pulse waves in order tocalculate a pulse transit time.

Suda et al., U.S. Pat. No. 5,788,634, describes a multi-purpose, clip-onsensor featuring a ‘gripper’ that includes an electrode pair and anoptical system operating in a transmission mode. The electrode pair andoptical system generate information that is processed outside of thesensor to make a blood pressure measurement.

Baruch et al., U.S. Pat. No. 6,723,054, describes an arm-worn systemfeaturing two optical systems that measure two independent signals froma patient's arm. A processor calculates mathematical derivatives of thesignals to derive a pulse transit time which can be used to calculateblood pressure.

Suga et al., U.S. Pat. No. 5,316,008, describes a wrist watch thatfeatures both optical and electrical sensors for measuring signals froma patient. During operation, the patient wears the wrist watch on onewrist, and places fingers from an opposing hand on the optical andelectrical sensors. A pulse transit time is extracted from the signalsand then used to calculate a blood pressure.

SUMMARY OF THE INVENTION

In one aspect, the invention features a monitoring device that measuresa patient's vital signs (e.g. blood pressure). The device features afirst sensor configured to attach to a first portion of the patient'sbody (e.g. a finger). The sensor includes: i) a first electrodeconfigured to generate a first electrical signal from the first portionof the patient's body; ii) a first light-emitting component; and iii) afirst photodetector configured to receive radiation from the firstportion of the patient's body and generate a first optical waveformafter the radiation is emitted by the first light-emitting component.The device also features a second sensor, configured to attach to asecond portion of the patient's body (e.g. a finger on the oppositehand), that includes essentially the same components. An amplifiersystem, in electrical contact with the first and second electrodes,receives first and second electrical signals from the two sensors togenerate an electrical waveform. A processor, in electrical contact withthe amplifier system, receives the electrical waveform, the firstoptical waveform, and the second optical waveform. The processor runscomputer code that processes the input waveforms with an algorithm todetermine at least one of the patient's vital signs, and mostparticularly blood pressure.

In embodiments, the computer code i) determines a time delay between thefirst optical waveform and the electrical waveform; and ii) processesthe time delay to determine a blood pressure value. In otherembodiments, the computer code i) determines a first time delay betweenthe first optical waveform and the electrical waveform; ii) determines asecond time delay between the second optical waveform and the electricalwaveform; and iii) processes at least one (or both) of the first andsecond time delays to determine a blood pressure value. In still otherembodiments, the computer code i) determines a time delay between thefirst and second optical waveforms; and ii) process the time delay todetermine a blood pressure value.

In another aspect, the invention features a device for measuring apatient's vital signs (e.g., blood pressure) that includes: 1) acontroller; 2) a first sensor, electrically connected to the controllerby a first electrical connection and configured to clip to a firstfinger located on a patient's first hand; and 3) a second sensor,electrically connected to the controller by a second electricalconnection and configured to clip to a second finger located on apatient's second hand. Both the first and second sensor include: i) anelectrical system configured to generate an electrical signal from theinserted finger; and ii) an optical system featuring at least one lightsource and a photodetector and configured to generate an optical signalfrom the inserted finger. A processor receives a processed electricalsignal generated from the first and second electrical signals and theoptical signal measured from each finger, and operates computer codethat processes the signals with an algorithm to determine at least oneof the patient's vital signs.

In embodiments, either (or both) the first or second sensor includes anadditional light-emitting component. In this case, the photodetector istypically located on a surface opposite the two light-emittingcomponents and configured so that radiation emitted by both thesecomponents passes through the patient's finger and into thephotodetector to generate separate signals. These signals, for example,can be processed by the processor to determine a pulse oximetry value.In embodiments, at least one of the light-emitting components isconfigured to emit infrared radiation (between, e.g., 800 and 1200 nm),red radiation (between, e.g., 600 and 700 nm), or green radiation(between, e.g., 500 and 550 nm) to generate an optical signal.

In other embodiments, one (or both) of the electrical connections is acable, e.g. a retractable cable.

The monitor can additionally include a simple wired or wirelessinterface that sends vital-sign information to a personal computer. Forexample, the device can include a Universal Serial Bus (USB) connectorthat connects to the computer's back panel. Once a measurement is made,the device stores it on an on-board memory and then sends theinformation through the USB port to a software program running on thecomputer. Alternatively, the device can include a short-range radiointerface (based on, e.g., Bluetooth or 802.15.4) that wirelessly sendsthe information to a matched short-range radio within the computer. Thesoftware program running on the computer then analyzes the informationto generate statistics on a patient's vital signs (e.g., average values,standard deviation, beat-to-beat variations) that are not available withconventional devices that make only isolated measurements. The computercan then send the information through a wired or wireless connection toa central computer system connected to the Internet.

The central computer system can further analyze the information, e.g.display it on an Internet-accessible website. In this way medicalprofessionals can characterize a patient's real-time vital signs duringtheir day-to-day activities, rather than rely on an isolated measurementduring a medical check-up. For example, by viewing this information, aphysician can delineate between patients exhibiting white coat syndromeand patients who truly have high blood pressure. Physicians candetermine patients who exhibit high blood pressure throughout theirday-to-day activities. In response, the physician can prescribemedication and then monitor how this affects the patient's bloodpressure.

These and other advantages of the invention will be apparent from thefollowing detailed description and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show schematic drawings of the hand-held vital signmonitor according to the invention operating in, respectively, one-timeand continuous modes;

FIGS. 2A, 2B, and 2C show, respectively, graphs of optical andelectrical waveforms generated with a first sensor, a second sensor, andoptical waveforms generated from both the first and second sensorsincluded in the monitor of FIGS. 1A and 1B;

FIG. 3 shows a schematic drawing of a patient characterized by themonitor of FIGS. 1A and 1B with blood flowing on their left andright-hand sides;

FIG. 4 shows a schematic front view of the first and second fingersensors included in the monitor of FIGS. 1A and 1B;

FIGS. 5A and 4B show schematic side views of the finger sensors of FIG.4 in, respectively, open and closed configurations;

FIGS. 6A and 6B show schematic top views of, respectively, top andbottom portions of the finger sensors of FIG. 4;

FIGS. 7A and 7B show schematic top views of, respectively, top andbottom portions of a patch sensor used in place of the finger sensors ofFIG. 4;

FIG. 8 shows a schematic view of the patch sensor of FIGS. 7A and 7Battached to the patient's hand;

FIG. 9 shows a schematic view of three patch sensors of FIGS. 7A and 7Battached to the patient's body;

FIGS. 10A and 10B show schematic views of, respectively, front and backsurfaces of the monitor of FIGS. 1A and 1B; and

FIG. 11 shows a schematic drawing of an in-hospital information systemoperating with the monitor of FIGS. 1A and 1B.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1A and 1B show two preferred embodiments of the invention whereina hand-held vital sign monitor 10 measures vital sign information suchas systolic and diastolic blood pressure, heart rate, pulse oximetry,temperature, ECG, and an optical plethysmograph from a patient 5. Usinga ‘bilateral’ measurement technique described in detail below, themonitor 10 measures blood pressure values without using a conventionalcuff-based system, and without requiring a complex calibrationprocedure. Specifically, blood pressure measurements are made with atechnique referred to herein as bilateral pulse transit time, or ‘BPTT’,which is described in more detail in the co-pending patent applicationentitled ‘SYSTEM FOR MEASURING VITAL SIGNS USING BILATERAL PULSE TRANSITTIME’, U.S. Ser. No. 11/420,652, filed May 26, 2006, the contents ofwhich are incorporated herein by reference.

The same monitor 10 measures vital sign information in two differentmodes: 1) a one-time mode (FIG. 1A) wherein the monitor 10 makes andstores a single measurement from a patient; and 2) a continuous mode(FIG. 1B) wherein the monitor 10 periodically measures and wirelesslytransmits multiple measurements from the patient over an extended periodof time. In this way, a single monitor can be used in a wide variety ofin-hospital settings, such as characterizing patients requiring just asingle vital sign measurement (e.g., patients waiting in a medicalclinic) to those requiring more sophisticated continuous monitoring(e.g., critically ill patients in a hospital telemetry ward). Themonitor 10 typically features dimensions and a user interface similar tothose of a conventional personal digital assistant (‘PDA’), and is smallenough to fit inside a medical professional's pocket or be worn on apatient's body. The monitor 10 features no cuffs and minimal externalwiring to simplify operation.

In the one-time mode, two sensors 15 a, 15 b, each featuring a ‘fingerclip’ form factor and described in more detail with reference to FIGS.4, 5A, 5B, 6A, and 6B, connect through cables 13, 14 to the monitor 10.The finger clip sensors 15 a, 15 b feature both optical and electricalmeasurement systems and easily clip onto fingers on the patient's leftand right hands to form a ‘bilateral’ configuration, described in moredetail below. In this configuration, each finger clip sensor measures,respectively, optical and electrical waveforms similar to thosedescribed with reference to FIGS. 2 and 3. The optical measurementsystem features a common photodetector and two independentlight-emitting systems: 1) an LED emitting green radiation that measuresa single optical waveform in a reflection-mode geometry; and 2) a pairof LEDs emitting red and infrared radiation that measure separateoptical waveforms in a transmission-mode geometry. The electricalmeasurement system within each finger clip sensor 15 a, 15 b features asingle electrode, typically composed of a conventional electrodematerial such as brass, stainless steel, or silver/silver chloride. Theelectrode may additionally include an impedance-matching component, suchas a conductive gel or rubber, or a disposable component.

During operation, the sensor simultaneously measures optical waveformsusing both the reflection and transmission-mode optical systems, alongwith electrical signals using the above-described electrodes. Thisinformation passes from the sensors 15 a, 15 b, through the cables 13,14, and to the monitor 10. The monitor 10 features a first amplifiersystem and electrical filter that processes the optical waveforms fromboth fingers to improve their signal-to-noise ratios, and a secondamplifier system and electrical filter that processes the electricalsignals from both fingers to generate a single electrical waveform,similar to a conventional single-lead ECG. An analog-to-digitalconverter, typically integrated within a microprocessor within themonitor, digitizes the optical and electrical waveforms to generateseparate arrays of data points which can then be further processed.Specifically, computer algorithms in the monitor 10 the process thedigitized optical and electrical waveforms measured in the bilateralconfiguration as described in more detail below to determine thepatient's vital signs.

In the continuous mode, disposable adhesive patch sensors 20 a, 20 b, 20c attach directly to the patient's chest and arm, and connect to eachother and a belt-worn monitor 10′ through the cables 13, 14. The patchsensors 20 a, 20 b, 20 c, described in more detail with reference toFIG. 7A and 7B, include both optical and electrical measurement systemssimilar to the finger clip sensors described above. Specifically, thepatch sensors 20 a, 20 b, 20 c include green, red, and infrared LEDs anda common photodetector. The LEDs and photodetector are configured sothat, when the patch sensor attaches to the patient's finger (e.g.,patch sensor 20 c), the green LED and photodetector measure an opticalwaveform using a reflection-mode geometry, and the red and infrared LEDsand the photodetector measure optical waveforms using atransmission-mode geometry. This geometry is shown in more detail inFIG. 8. When the patch sensor is attached to the patient's chest, thegreen LED and photodetector measure an optical waveform in areflection-mode geometry, while measurements in a transmission modegeometry are typically not possible. Regardless of their positioning,electrodes within the adhesive patch sensors 20 a, 20 b, 20 c measureelectrical signals from the patient's finger and chest.

Optical waveforms and electrical signals measured by the adhesive patchsensors 20 a, 20 b, 20 c are processed by circuitry within the belt-wornmonitor 10′ to determine the patient's vital signs. Both the monitor 10and the belt-worn monitor 10′ additionally include a short-rangewireless system that transmits the vital signs to a number of possibledevices, each of which includes a matched short-range wireless system.For example, the belt-worn monitor 10′ can transmit vital signinformation to: 1) the hand-held monitor 10 (as indicated by arrow 16a); 2) a remote computer 33 (as indicated by arrow 16 b); or 3) awall-mounted display 30 (e.g., an LCD or plasma screen, as indicated byarrow 16 c). The belt-worn monitor 10′ can transmit vital signinformation in response to a command (sent, e.g., from the hand-heldmonitor 10), or periodically according to one or more pre-programmedvalues.

Referring to FIGS. 2A, 2B, 2C, the monitor 10 measures blood pressureusing BPTT by processing optical waveforms 29A, 29B and electricalwaveforms 31A, 31B measured simultaneously from each side of thepatient's body. Each waveform includes a ‘pulse’ that corresponds toeach of the patient's heartbeats. In the electrical waveforms 31A, 31B,this pulse represents electrical signals generated by the beating heart,and includes a sharply varying ‘peak’ within a conventional QRS complexof the ECG. In contrast, for the optical waveforms 29A, 29B, the pulsevaries more gradually and represents a time-dependent volumetric changein an underlying artery. A microprocessor in the monitor 10 calculates apulse transit time (‘PTT’), described in more detail below, by analyzinga time difference ΔT between a point on the optical 29A, 29B andelectrical 31A, 31B waveforms (e.g., ΔT between the peaks of thesewaveforms). Specific points on the waveforms, such as their maxima orminima, can be determined by taking a first or second derivative of thewaveform. ΔT measured from the optical waveform 29A from the patient'sleft index finger and the electrical waveform 31A is shown in FIG. 2A(labeled ΔT_(L)). Similarly, ΔT measured from the optical waveform 29Bfrom the right index finger and the electrical waveform 31B is shown inFIG. 2B (labeled ΔT_(R)).

In the one-time mode, a BPTT measurement processes PTTs measured withthe finger clip sensors from the patient's left finger (ΔT_(L)) andright finger (ΔT_(R)) to make an accurate measurement of blood pressure.Specifically, PTT depends on several factors, including blood pressure,distance between the heart and the portion of the body where the opticalwaveform is measured (e.g., the patient's finger), and properties of thepatient's vasculature (e.g., arterial compliance, size, and stiffness).

BPTT as described herein can potentially improve the accuracy of anormal PTT measurement. For example, as shown in FIG. 3, a patient'sheart 48 is typically located in a relatively well-defined position onthe left-hand side of their chest cavity. With each heartbeat, bloodsimultaneously flows along a right-hand vascular pathlength 44A to reacha point 42A on the patient's right hand, and along a left-hand vascularpathlength 44B to reach a point 42B on the patient's left hand. Theright-hand vascular pathlength 44A typically differs from the left-handvascular pathlength 44B. The difference in pathlengths can correlatewith the patient's biometric parameters (e.g., height, arm span). Thedifference in pathlengths and corresponding difference in PTTs can beused in the calculation of the patient's vital signs (e.g., bloodpressure), as is described in more detail below.

Following a heartbeat, electrical impulses travel essentiallyinstantaneously from the patient's heart to electrodes within eachfinger clip or adhesive patch sensor, which detect it to generate anelectrical waveform. At a later time, a pressure wave induced by thesame heartbeat simultaneously propagates through the patient'sright-hand 44A and left-hand 44B vascular pathlengths. At points 42A,42B on the patient's left and right hands, elastic arteries within thesevascular pathlengths increase in volume due to the pressure wave.Ultimately the pressure wave arrives at a portion of the arteryunderneath the LED and photodetector within each sensor. These opticscombine to form an optical system that detects the pressure wave bymeasuring a time-dependent change in optical absorption. The propagationtime of the electrical impulse is independent of blood pressure, whereasthe propagation time of the pressure wave depends strongly on pressure,as well as properties of the patient's arteries.

Referring again to FIGS. 2A, 2B, and 2C, during a BPTT measurement,optical sensors within the right and left finger clip or adhesive patchsensors simultaneously measure optical waveforms 29A, 29B, whileelectrodes in the sensors measure electrical waveforms 31A, 31B. Theoptical waveforms 29A, 29B are unique to each area underneath thesensor, while the electrical waveforms 31A, 31B are identical, and aredetermined by combining electrical signals from multiple sensors. Amicroprocessor within the monitor runs an algorithm that analyzes thetime difference ΔT_(L,R) between the arrivals of these signals, i.e. therelative occurrence of the optical 29A, 29B and electrical 31A, 31Bwaveforms for both the right-hand 44A and left-hand 44B vascular system.The microprocessor additionally analyzes the time difference ΔT_(O)between the arrival of the two optical signals 29A, 29B.

In a BPTT measurement, the asymmetric position of the heart, coupledwith the assumption that blood pressure is equivalent along theleft-hand 44B and right-hand 44A vascular pathlengths, means the PTT forthe right-hand pathlength 44A will typically be slightly longer than thePTT for the left-hand pathlength 44B. This time difference, ΔPTT, is thedifference between ΔT_(L) and ΔT_(R) (i.e. ΔPTT=ΔT_(R)−ΔT_(L)) and canbe used to estimate the patient's arm length if a speed of thepropagating pressure pulse, called a pulse wave velocity (‘PWV’) isassumed. Inclusion of arm length in a PTT-based measurement typicallyimproves accuracy for both systolic and diastolic blood pressure. Use ofBPTT to determine ΔPTT means arm length can be estimated without havingto enter it through a software user interface. Alternatively, the armlength can be entered into a user interface associated with the monitor,and then processed along with ΔPTT to calculate a PWV. This is done byusing the above-described assumptions describing the asymmetricalposition of the heart. Blood pressure is known to depend strongly on PWV(typically an increase in PWV indicates an increase in blood pressure),and thus a measured PWV value can be compared to a look-up table storedin memory to calculate blood pressure. Alternatively, a mathematicalalgorithm, such as a predetermined relationship (e.g., a linearrelationship) between PWV and blood pressure, may be used to calculatesubsequent blood pressure values.

Referring to FIG. 2C, in another embodiment the time difference ΔT_(O)between points (e.g., peaks) on two optical signals measured atdifferent locations on the patient's body can be processed to determinea PWV. For example, separate patch sensors 20 b, 20 c located,respectively, on the patient's chest and finger can measure the arrivalof a pulse wave following each heart beat. As described above, thedistance between the patch sensors 20 b, 20 c divided by the timedifference ΔT_(O) yields a PWV, which can then be compared to a look-uptable stored in memory or processed with a more sophisticated algorithmto calculate blood pressure. For example, the algorithm may use apredetermined relationship (e.g. a linear relationship) between PWV andblood pressure to calculate subsequent blood pressure values.

In addition, with the BPTT measurement, optical waveforms measured fromthe patient's left and right hands or ΔPTT can be compared to determineslight differences in waveform shape. These slight differences can thenbe processed to achieve a more accurate calculation of the patient'sblood pressure. For example, the differences in left and right waveformshapes or arrival times measured as described above can be used todetermine a particular mathematical model for calculating blood pressurefrom a patient, or alternatively properties other than blood pressure.An abnormally high or negative ΔPTT, for example, may indicate aprofound difference between a patient's right-hand 44A and left-hand 44Bvascular pathlength. Such a difference, for example, may indicate thepresence of an occlusion (e.g., a blood clot) or stenosis in eithervascular pathlength. In related embodiments, the ΔPTT or waveform shapedifferences may be used to estimate a patient's arterial compliance. Forexample, the differences in the patient's right-hand 44A and left-hand44B vascular pathlengths will result in corresponding differences in thediffusion of light-absorbing blood cells in the two pathlengths. Thesedifferences in cellular diffusion are observed as differences in theshapes of the optical waveforms 29A and 29B. The waveform shapedifferences will depend on the arterial compliance along the right-hand44A and left-hand 44B vascular pathlengths. For example, the opticalsignals (29A, 29B) shown in FIGS. 2A, 2B, 2C typically feature a mainpeak and a secondary peak, where the secondary peak is typicallyclassified as a ‘dichrotic notch’. Studies published in the literaturedescribe how the dichrotic notch, particularly when analyzed by taking asecond derivative of the plethysmogram, relates to vascular compliance(see, e.g., ‘Assessment of Vasoactive Agents and Vascular Aging by theSecond Derivative of Photoplethysmogram Waveform’, Takazawa et. al,Hypertension 32: 365-370, 1998; the contents of which are incorporatedherein by reference). Arterial compliance determined using this oranother method can then be used to group patients having similararterial properties. An algorithm can then process ΔPTT or PWV valuesfor patients in a particular group, or compare these values topredetermined look-up tables, to make a blood pressure measurement. Forexample, the algorithm may use a predetermined relationship (e.g. alinear relationship) between PWV or ΔPTT and blood pressure to calculatesubsequent blood pressure values.

Referring again to FIGS. 2A, 2B, and 2C, in yet another embodiment,processing the electrical waveform 31A, 31B and optical waveforms 29A,29B can be used to estimate a property called pre-ejection period(‘ΔT_(PEP)’), which is the time delay between the beginning of apatient's heart beat and the beginning of the patient's cardiac stroke.Specifically, both ΔT_(R) and ΔT_(L) depend on ΔT_(PEP) and the time ittakes the pressure pulse to leave the heart and arrive at the opticalsystem underneath a corresponding sensor. As shown in FIG. 2C, this timedifference, referred to as ΔT_(O), can be measured directly from patchsensors located near the patient's heart and finger. If the patch sensoris located on the patient's right hand, ΔT_(R)−AT_(O)=ΔT_(PEP), while ifthe patch sensor is located on the patient's left handΔT_(L)−ΔT_(O)=ΔT_(PEP). ΔT_(PEP) correlates with the patient's systolicfunction, with a shorter ΔT_(PEP) typically indicating a relativelyhealthy systolic function. A measured ΔT_(PEP) can be used inconjunction with the time difference between a feature on the electricalwaveform and one or more features on one or more optical waveforms toimprove the accuracy of the calculated PTT and corresponding bloodpressure. In particular, it has been shown in previous studies thatsystolic blood pressure can correlate better to a ΔPTT value, whereasdiastolic blood pressure and mean arterial blood pressure can correlatebetter to a ΔPTT value corrected for ΔT_(PEP), i.e. ΔPTT−ΔT_(PEP) (see,e.g., ‘Pulse transit time measured from the ECG: an unreliable marker ofbeat-to-beat blood pressure’, Payne et. al, J. Appl. Physiol 100:136-141, 2006; the contents of which are incorporated herein byreference). ΔT_(PEP) values may also vary with respiration andinspiration, thereby affecting the measured blood pressure. For thisreason, in embodiments, computer code operating in the monitor describedabove can first process two optical waveforms to estimate ΔT_(PEP). Oncethis is done, the computer code can determine ΔPTT and ΔPTT−ΔT_(PEP),which are then used to calculate, respectively, systolic and diastolicblood pressure.

FIGS. 4, 5A, 5B, 6A, and 6B show the above-described finger clip sensors15 a, 15 b of FIG. 1A in more detail. As described above, finger clipssensors 15 a, 15 b are typically used in a one-time measurement mode.Each finger clip sensor 15 a, 15 b is designed to gently clip onto anindex finger on the patient's left and right hands, and features a topportion 70 a, 70 b connected to a bottom portion 72 a, 72 b by aspring-loaded backing portion 62 a, 62 b. This configuration ensuresthat, during operation, each finger clip sensor secures to the patient'sfinger and blocks out ambient light, thereby increasing thesignal-to-noise ratio of both the optical and electrical measurements.As described above, the bottom portion 72 a, 72 b features an electrodematerial 60 a, 60 b that contacts a bottom portion of the patient'sfinger when the finger clip sensor is closed. The electrode material 60a, 60 b is typically a metal, such as brass or copper, or a conventionalelectrode such as silver/silver chloride. The electrode material 60 a,60 b may also include an impedance-matching material, such as aconductive gel or rubber. Electrical signals measured with electrodematerials 60 a, 60 b from the left 15 a and right 15 b finger clipsensors pass through cables 13, 14 to the monitor, where they areprocessed with an amplifier circuit and then digitized to generate anelectrical waveform similar to a conventional ECG. Unlike the opticalwaveforms, which specifically correspond to each blood flowing in eachindex finger, a single electrical waveform is determined by jointlyprocessing electrical signals measured from each index finger using theamplifier circuit.

The bottom portion 72 a, 72 b of the finger clip sensor 15 a, 15 badditionally includes a photodiode 66 a, 66 b and a green LED 68 a, 68 bdisposed on the same surface, and typically separated from each other byabout 1-2 mm. During operation, radiation from the green LED 68 a, 68 breflects off the patient's finger and its underlying arteries togenerate reflected radiation, which the photodiode 66 a, 66 b detects togenerate a time-dependent optical waveform. This waveform is measured ina reflection-mode geometry, and because it is not used to calculatepulse oximetry, can typically be measured at a relatively high frequency(e.g., several kHz) and resolution (8-16-bit). Typically the photodiode66 a, 66 b and green LED 68 a, 68 b are seated below a soft rubbermaterial so that they don't make direct contact with skin on the bottomsurface of the patient's finger. The top portion 70 a, 70 b includes ared LED 64 a, 64 b and an infrared LED which sequentially emit radiationthat, during operation, transmits through the patient's index finger andits underlying arteries. Some radiation that passes through the arteriesexposes the photodiode 66 a, 66 b, which in response generates a pair oftime-dependent optical waveforms (one from each of the red and infraredLEDs). These waveforms are measured in a transmission-mode geometry.During operation, the optical waveforms measured in both transmissionand reflection modes pass through the cables 13, 14 to the monitor,where they are processed as described above to measure the patient'svital signs. Blood pressure values are calculated as described above.Heart rate values can be calculated by processing the optical andelectrical waveforms using techniques known in the art. Pulse oximetryvalues can be calculated by collectively processing waveforms generatedby the red and infrared LEDs using techniques know in the art.

FIGS. 7A, 7B, 8 and 9 show the adhesive patch sensors 20 a, 20 b, 20 cof FIG. 1B in more detail. As described above, the adhesive patchsensors 20 a, 20 b, 20 c are typically used in a continuous measurementmode. Each sensor features a green LED 88 positioned proximal to aphotodiode 86, both of which are disposed on a flexible printed circuitboard 87. When the sensor is attached to a patient, these opticalcomponents generate an optical waveform as described above. Ahorseshoe-shaped metal electrode 80 formed on top of the flexibleprinted circuit board 87 surrounds these optical components andgenerates an electrical signal that, when processed in concert withanother electrical signal from a separate electrode, generates anelectrical waveform. Red 84 and infrared 85 LEDs are additionallymounted on an opposite end of the flexible printed circuit board. Whenthe sensor is attached to a patient's finger, as shown in FIG. 8, thered 84 and infrared 85 LEDs generate radiation that passes through thefinger and into the photodiode 86, as described above, to generateseparate optical waveforms in a transmission-mode geometry. On its outersurface the sensor includes a snap connector 89 that allows it to easilyattach and detach to a cable 13. All electrical signals and opticalwaveforms, once generated, pass through the cable 13 to the monitor,which analyzes them as described above to measure a patient's vital signinformation. The patch sensor 20 additionally features an adhesivecomponent 91, similar to that in a common band-aid or ECG electrode,which adheres to the patient's skin and secures the sensor in place tominimize the effects of motion.

Both the cable 13 and snap connector 89 include matched electrical leadsthat supply power and ground to the LEDs 84, 85, 88, photodetector 86,and electrode 80. When the patch sensor 20 is not measuring optical andelectrical waveforms, the cable 13 unsnaps from the snap connector 89,while the sensor 20 remains adhered to the patient's skin. In this way asingle sensor can be used for several days. After use, the patientremoves and then discards the sensor 20.

FIGS. 10A and 10B show, respectively, front and back surfaces of themonitor 10. The front surface (FIG. 10A) features a touch-screen display100 rendering a graphical user interface that operates in both one-timeand continuous modes. A removable stylus 108 is housed in a slot on atop surface of the monitor and is used to operate the user interfacethrough the touch-screen display 100. The monitor 10 typically includesseparate antennae 102, 104 for, respectively, short-range communications(for, e.g., part-15 or 802.11-based networks) and long-rangecommunications (for, e.g., CDMA networks). The antenna 102 forshort-range communication typically communicates with peripheraldevices, such as the belt-worn monitor, a wireless scale, chest strap,thermal printer, external monitor, or local personal computer. Theantenna 104 for long-range communications is typically used to sendinformation through a wireless network to an Internet-based computersystem. The monitor also includes an on/off button 112 and a USBconnector 110 for downloading information to a personal computer andrecharging the monitor's battery through a cable.

On its back surface (FIG. 10B) the monitor 10 includes a mechanicalmechanism 114 that retracts both cables 13, 14 when they're not in use.In this way the monitor can be kept as compact as possible with minimalexternal components. Alternatively, the mechanical mechanism 114 can bereplaced with a simple connector that mates with a connector terminatingboth cables 13, 14. In other embodiments, the monitor can also include abar code scanner 115 that reads conventional bar-coded information from,e.g., a patient's wrist band. Typically the bar code scanner 115connects to a microprocessor through a serial interface. In otherembodiments, a thermometer 116 for measuring body temperature connectsto the monitor 10 through either a wired or wireless interface.

FIG. 11 shows a preferred embodiment of an Internet-based system 152that operates in concert with the hand-held monitor 10 and body-wornmonitor 10′ to send information from a patient 130 to an in-hospitalinformation system 171. Using the hand-held monitor 10, a medicalprofessional 131 collects vital sign information from the patient'sbody-worn monitor 10′ through a short-range wireless connection 16a.Alternatively, the body-worn monitor 10′ automatically transmits vitalsign information in a continuous or near-continuous manner. In bothcases, using an internal wireless modem, information travels from eitherthe hand-held monitor 10 or body-worn monitor 10′ through a wirelessinterface 16 b to a wireless network 154 (e.g., either a nation-wide orlocal wireless network), and from there to a web site 166 hosted on anInternet-based host computer system 33. A secondary computer system 169accesses the website 166 through the Internet 167. A wireless gateway155 connects to the host computer system 33 and ultimately to thewireless network 154, and receives data from one or more monitors, asdiscussed below. The host computer system 33 includes a database 163 anda data-processing component 168 for, respectively, storing and analyzingdata sent from the monitor. The host computer system 33, for example,may include multiple computers, software systems, and othersignal-processing and switching equipment, such as routers and digitalsignal processors. The wireless gateway 155 preferably connects to thewireless network 154 using a TCP/IP-based connection, or with adedicated, digital leased line (e.g., a VPN, frame-relay circuit ordigital line running an X.25 or other protocols). The host computersystem 33 also hosts the web site 166 using conventional computerhardware (e.g. computer servers for both a database and the web site)and software (e.g., web server and database software). To connect to thein-hospital information system 171 (e.g., a system for electronicmedical records), the host computer system 33 typically includes a webservices interface 170 that sends information using an XML-based webservices link to a computer associated with the in-hospital informationsystem 171. Alternatively, the wireless network 154 may be anin-hospital wireless network (e.g., a network operating Bluetooth™,802.11a, 802.11b, 802.11g, 802.15.4, or ‘mesh network’ wirelessprotocols) that connects directly to the in-hospital information system171. In this embodiment, a nurse working at a central nursing stationcan quickly view the vital signs of the patient using a simple computerinterface.

To view information remotely, the patient or medical professional canaccess a user interface hosted on the web site 166 through the Internet167 from a secondary computer system 169, such as an Internet-accessiblehome computer. The system may also include a call center, typicallystaffed with medical professionals such as doctors, nurses, or nursepractitioners, whom access a care-provider interface hosted on the samewebsite 166.

Other embodiments are also within the scope of the invention. Forexample, PTT can be used to first determine mean arterial pressure (MAP)as opposed to systolic blood pressure (BP SYS) or diastolic bloodpressure (BP DIA). In this case, a predetermined relationship betweenPTT and MAP is established. In subsequent measurements, PTT is measuredand used to calculate MAP. The optical waveform can then be analyzed toestimate pulse pressure (i.e., BP SYS−BP DIA), which can then be usedalong with MAP to estimate both BP SYS and BP DIA using the formula:

MAP=BP SYS+⅓(BP SYS−BP DIA)

In still other embodiments, the body-worn monitor can optionally be usedto determine the patient's location using embedded position-locationtechnology (e.g., GPS, network-assisted GPS, or Bluetooth™, 802.11-basedlocation system). In situations requiring immediate medical assistance,the patient's location, along with relevant vital sign information, canbe relayed to emergency response personnel.

Still other embodiments are within the scope of the following claims.

1. A method for measuring a blood pressure of a user, the methodcomprising: generating a first optical waveform from a signal from afirst optical sensor positioned on the user; generating a second opticalwaveform from a signal from a second optical sensor positioned on theuser, the second optical waveform generated simultaneously with thefirst optical waveform, the second optical sensor positioned adistinguishable distance from the first optical sensor on the user;generating an electrical waveform from a signal from a first electrodepositioned in proximity with the first optical sensor and a signal froma second electrode positioned in proximity with the second opticalsensor; determining a first pulse transit time, the first pulse transittime calculated by processing the electrical waveform and the firstoptical waveform; determining a second pulse transit time, the secondpulse transit time calculated by processing the electrical waveform andthe second optical waveform; and processing the first pulse transit timeand the second pulse transit time to determine a blood pressure valuefor the user.
 2. The method of claim 1, wherein determining the firstpulse transit time further comprises determining a first point on thefirst optical waveform or a processed version thereof, determining asecond point on the electrical waveform or a processed version thereof,and determining a time difference between the first and second points.3. The method of claim 2, further comprising determining a mathematicalderivative of the first optical waveform, and then determining the firstpoint from a maximum value of the mathematical derivative of the firstoptical waveform.
 4. The method of claim 1, wherein determining thesecond pulse transit time further comprises determining a first point onthe second optical waveform or a processed version thereof, determininga second point on the electrical waveform or a processed versionthereof, and then determining a time difference between the first andsecond points.
 5. The method of claim 4, further comprising determininga mathematical derivative of the second optical waveform, and thendetermining the first point from a maximum value of the mathematicalderivative of the second optical waveform.
 6. The method of claim 1,wherein the processing further comprises comparing at least one of thefirst pulse transit time and the second pulse transit time to apredetermined mathematical relationship between pulse transit time andblood pressure.
 7. The method of claim 1, further comprising processingat least one of the first optical waveform and the second opticalwaveform to determine a property related to arterial compliance.
 8. Themethod of claim 7, further comprising taking a second mathematicalderivative of at least one of the first optical waveform and the secondoptical waveform, and then processing the second derivative to determinea property related to arterial compliance.
 9. The method of claim 1,further comprising comparing the first optical waveform and the secondoptical waveform to determine a property related to blood flow along twodifferent arterial pathways of the user.
 10. The method of claim 1,further comprising processing the first optical signal or a processedversion thereof and the second optical signal or a processed versionthereof to determine a third pulse transit time.
 11. The method of claim10, further comprising processing the third pulse transit time todetermine a blood pressure value for the user.
 12. A method formeasuring a blood pressure of a user, the method comprising: generatinga plurality of optical waveforms, each of the plurality of opticalwaveforms generated from a signal from an optical sensor, wherein eachoptical sensor is positioned a distinguishable amount from any otheroptical sensor on the user; generating an electrical waveform from aplurality of signals, each of the plurality of signals generated from anelectrode positioned in proximity to an optical sensor; determining aplurality of pulse transit times, each of the plurality of pulse transittimes calculated by processing the electrical waveform and at least twooptical waveforms; processing each of the plurality of pulse transittimes to determine a blood pressure value for the user.
 13. The methodof claim 12, further comprising determining a first pulse transit timeby processing a first optical waveform and the electrical waveform, anda second pulse transit time by processing a second optical waveform andthe electrical waveform.
 14. The method of claim 13, wherein determiningthe first pulse transit time further comprises determining a first pointon the first optical waveform or a processed version thereof,determining a second point on the electrical waveform or a processedversion thereof, and determining a time difference between the first andsecond points.
 15. The method of claim 14, further comprisingdetermining a mathematical derivative of the first optical waveform, andthen determining the first point from a maximum value of themathematical derivative of the first optical waveform.
 16. The method ofclaim 13, wherein determining the second pulse transit time furthercomprises determining a first point on the second optical waveform or aprocessed version thereof, determining a second point on the electricalwaveform or a processed version thereof, and then determining a timedifference between the first and second points.
 17. The method of claim16, further comprising determining a mathematical derivative of thesecond optical waveform, and then determining the first point from amaximum value of the mathematical derivative of the second opticalwaveform.
 18. The method of claim 13, wherein the processing furthercomprises comparing at least one of the first pulse transit time and thesecond pulse transit time to a predetermined mathematical relationshipbetween pulse transit time and blood pressure.
 19. The method of claim13, further comprising processing the first optical signal or aprocessed version thereof and the second optical signal or a processedversion thereof to determine a third pulse transit time.
 20. The methodof claim 19, further comprising processing the third pulse transit timeto determine a blood pressure value for the user.
 21. A method formeasuring a blood pressure of a user, the method comprising: generatinga first optical waveform from a signal from a first optical sensorpositioned on a finger of a right-hand of the user; generating a secondoptical waveform from a signal from a second optical sensor, the secondoptical waveform generated simultaneously with the first opticalwaveform, the second optical sensor positioned on a finger of aleft-hand of the user; generating an electrical waveform from a signalfrom a first electrode positioned in proximity with the first opticalsensor and a signal from a second electrode positioned in proximity withthe second optical sensor; determining a first pulse transit time, thefirst pulse transit time calculated by processing the electricalwaveform and the first optical waveform; determining a second pulsetransit time, the second pulse transit time calculated by processing theelectrical waveform and the second optical waveform; and processing thefirst pulse transit time and the second pulse transit time to determinea blood pressure value for the user.
 22. A method for measuring a bloodpressure of a user, the method comprising: generating a first opticalwaveform from a signal from a first optical sensor positioned on theuser; generating a second optical waveform from a signal from a secondoptical sensor positioned on the user, the second optical waveformgenerated simultaneously with the first optical waveform, the secondoptical sensor positioned a distinguishable amount from the firstoptical sensor on the user; generating an electrical waveform from asignal from a first electrode positioned in proximity with the firstoptical sensor and a signal from a second electrode positioned inproximity with the second optical sensor; determining a pulse transittime, the pulse transit time calculated by processing the first opticalwaveform and the second optical waveform; and processing the pulsetransit time to determine a blood pressure value for the user.